Radiative collisional heating at the Doppler limit for laser-cooled magnesium atoms

We report Monte Carlo wave function simulation results on cold collisions between magnesium atoms in a strong red-detuned laser field. This is the normal situation e.g. in magneto-optical traps (MOT). The Doppler limit heating rate due to radiative collisions is calculated for Mg-24 atoms in a magneto-optical trap based on the singlet S_0 - singlet P_1 atomic laser cooling transition. We find that radiative heating does not seem to affect the Doppler limit in this case. We also describe a channelling mechanism due to the missing Q branch in the excitation scheme, which could lead to a suppression of inelastic collisions, and find that this mechanism is not present in our simulation results due to the multistate character of the excitation process.Comment: 4 pages, RevTeX 4; v2 contains minor revisions based on referee comments (5 pages

Inert states of spin-S systems

We present a simple but efficient geometrical method for determining the inert states of spin-S systems. It can be used if the system is described by a spin vector of a spin-S particle and its energy is invariant in spin rotations and phase changes. Our method is applicable to an arbitrary S and it is based on the representation of a pure spin state of a spin-S particle in terms of 2S points on the surface of a sphere. We use this method to find candidates for some of the ground states of spinor Bose-Einstein condensates.Comment: 4 pages, 2 figures, minor changes, references added, typos correcte

Center of mass rotation and vortices in an attractive Bose gas

The rotational properties of an attractively interacting Bose gas are studied using analytical and numerical methods. We study perturbatively the ground state phase space for weak interactions, and find that in an anharmonic trap the rotational ground states are vortex or center of mass rotational states; the crossover line separating these two phases is calculated. We further show that the Gross-Pitaevskii equation is a valid description of such a gas in the rotating frame and calculate numerically the phase space structure using this equation. It is found that the transition between vortex and center of mass rotation is gradual; furthermore the perturbative approach is valid only in an exceedingly small portion of phase space. We also present an intuitive picture of the physics involved in terms of correlated successive measurements for the center of mass state.Comment: version2, 17 pages, 5 figures (3 eps and 2 jpg

Atomic dynamics in evaporative cooling of trapped alkali atoms in strong magnetic fields

We investigate how the nonlinearity of the Zeeman shift for strong magnetic fields affects the dynamics of rf field induced evaporative cooling in magnetic traps. We demonstrate for the 87-Rb and 23-Na F=2 trapping states with wave packet simulations how the cooling stops when the rf field frequency goes below a certain limit (for the 85-Rb F=2 trapping state the problem does not appear). We examine the applicability of semiclassical models for the strong field case as an extension of our previous work [Phys. Rev. A 58, 3983 (1998)]. Our results verify many of the aspects observed in a recent $^{87}$Rb experiment [Phys. Rev. A 60, R1759 (1999)].Comment: 9 pages, RevTex, eps figures embedde

Strategic Utilization of the VR and AR Technologies for the African Cultural Heritage Promotion and Management

The importance and purpose of heritage preservation have been extensively discussed in tourism research and has also been linked with regional and national development strategies. Because of time degradation, human activities, and the overcrowding effect, heritage preservation and reconstruction efforts are becoming critical to ensure the sustainability of heritage sites and disseminate the history and the potential of a region or a country. Virtual reality (VR) and augmented reality (AR) offer useful applications in heritage preservation. This study aims to explore the potential of these interactive technologies to be applied in heritage preservation in Africa, introduce strategies and applications developed Egypt and Tunis but also from Oman, and Finland, and highlight their impact in regional and national socio-economic development. As members of the Time Machine Europe this paper analyzes previous experiences in global scale and aim is to contribute in large-scale digitalization projects in Europe but also world-wide

Temporal Interferometry: A Mechanism for Controlling Qubit Transitions During Twisted Rapid Passage with Possible Application to Quantum Computing

In an adiabatic rapid passage experiment, the Bloch vector of a two-level system (qubit) is inverted by slowly inverting an external field to which it is coupled, and along which it is initially aligned. In twisted rapid passage, the external field is allowed to twist around its initial direction with azimuthal angle $\phi (t)$ at the same time that it is inverted. For polynomial twist: $\phi (t) \sim Bt^{n}$. We show that for $n \geq 3$, multiple avoided crossings can occur during the inversion of the external field, and that these crossings give rise to strong interference effects in the qubit transition probability. The transition probability is found to be a function of the twist strength $B$, which can be used to control the time-separation of the avoided crossings, and hence the character of the interference. Constructive and destructive interference are possible. The interference effects are a consequence of the temporal phase coherence of the wavefunction. The ability to vary this coherence by varying the temporal separation of the avoided crossings renders twisted rapid passage with adjustable twist strength into a temporal interferometer through which qubit transitions can be greatly enhanced or suppressed. Possible application of this interference mechanism to construction of fast fault-tolerant quantum CNOT and NOT gates is discussed.Comment: 29 pages, 16 figures, submitted to Phys. Rev.

Exact Soliton-like Solutions of the Radial Gross-Pitaevskii Equation

We construct exact ring soliton-like solutions of the cylindrically symmetric (i.e., radial) Gross- Pitaevskii equation with a potential, using the similarity transformation method. Depending on the choice of the allowed free functions, the solutions can take the form of stationary dark or bright rings whose time dependence is in the phase dynamics only, or oscillating and bouncing solutions, related to the second Painlev\'e transcendent. In each case the potential can be chosen to be time-independent.Comment: 8 pages, 7 figures. Version 2: stability analysis of the dark solutio

Quantum and Semiclassical Calculations of Cold Atom Collisions in Light Fields

We derive and apply an optical Bloch equation (OBE) model for describing collisions of ground and excited laser cooled alkali atoms in the presence of near-resonant light. Typically these collisions lead to loss of atoms from traps. We compare the results obtained with a quantum mechanical complex potential treatment, semiclassical Landau-Zener models with decay, and a quantum time-dependent Monte-Carlo wave packet (MCWP) calculation. We formulate the OBE method in both adiabatic and diabatic representations. We calculate the laser intensity dependence of collision probabilities and find that the adiabatic OBE results agree quantitatively with those of the MCWP calculation, and qualitatively with the semiclassical Landau-Zener model with delayed decay, but that the complex potential method or the traditional Landau-Zener model fail in the saturation limit.Comment: 21 pages, RevTex, 7 eps figures embedded using psfig, see also http://www.physics.helsinki.fi/~kasuomin